KVM: riscv: selftests: Fix incorrect rounding in page_align()

KVM: riscv: selftests: Fix incorrect rounding in page_align()

The implementation of `page_align()` in `processor.c` calculates
alignment incorrectly for values that are already aligned. Specifically,
`(v + vm->page_size) & ~(vm->page_size - 1)` aligns to the *next* page
boundary even if `v` is already page-aligned, potentially wasting a page
of memory.

Fix the calculation to use standard alignment logic: `(v + vm->page_size
- 1) & ~(vm->page_size - 1)`.

Fixes: 3e06cdf10520 ("KVM: selftests: Add initial support for RISC-V 64-bit")
Reviewed-by: Andrew Jones <andrew.jones@linux.dev>
Signed-off-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20260109082218.3236580-4-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>